This invention relates to fluorescent lamps and, more particularly, to folded discharge fluorescent lamps and inter-channel isolation means.
In response to increasing energy costs, greater than average efforts have been expended in recent years on the development of more efficient lighting devices. In particular, it is appreciated that conventional fluorescent lighting is an efficient alternative to the incandescent lamp. However, for efficient operation, the ratio of the discharge path length to the discharge path diameter in a fluorescent lamp must be carefully selected to avoid decreasing lamp efficacy. In particular, this ratio of length-to-diameter (L/D) is typically between 10 and 90 for conventional fluorescent lamps. Accordingly, it should therefore be appreciated that these efficacy constraints have generally resulted in the long cylindrical fluorescent lamps that are now commonplace featues. However, efforts to replace conventional incandescent lamps with appropriately-rated fluorescent lamps have proven to be a significant manufacturing and engineering challenge.
For example, in U.S. Pat. No. 4,095,135, issued June 13, 1978 to Yamazaki et al., there is apparently described a spherical-bulb fluorescent lamp apparently solving some of the problems associated with folded discharge lamps. Similarly, in U.S. Pat. No. 4,196,374, issued Apr. 1, 1980 to Harald L. Witting, there is disclosed a compact folded discharge fluorescent lamp comprising a substantially cylindrical tapered envelope with correspondingly tapered partitions disposed within the envelope so as to define the folded discharge path. Other solutions to the problem of producing a compact fluorescent lamp have been solved by the use of so-called short arc fluorescent lamps possessing large envelope areas to reduce phosphor loading and specially-designed electrodes to maximize arc length and to minimize sputtering of cathode material which may otherwise occur in the low pressure environments employed in such lamps. See U.S. Pat. No. 4,093,893, issued June 6, 1978 to John M. Anderson.
One of the more significant approaches taken to the problem of developing compact fluorescent lamps is the use of the so-called folded discharge design in which the length of the discharge arc path is increased through the use of geometric means which force the arc into a convoluted path, often doubling back on itself, so as to increase the effective length of the discharge column, and, accordingly, to increase the value of the ratio L/D as discussed above. The most significant problem arising in the folded arc discharge concept, however, is the isolation of various parts of the folded discharge from other parts of the folded discharge. One solution to this problem appears to be disclosed in U.S. Pat. No. 4,191,907, issued March 4, 1980 to Rogoff. In this patent there is apparently disclosed a discharge bypassing prevention method employing partition panels including gaskets of feltlike material at the edges of the partition panels. A similar scheme appears to be disclosed in U.S. Pat. No. 4,184,101, issued Jan. 15, 1980 to Young. A still further example of such a gasket sealing design is shown in U.S. Pat. No. 4,182,975, issued Jan. 8, 1980 to Young. Other compact folded discharge lamps are also described in U.S. Pat. No. 4,173,730, issued Nov. 6, 1979 to Young et al. and also in U.S. Pat. No. 4,185,221, issued Jan. 22, 1980 to Young. However, all of these designs depend upon a relatively tight seal between partitioned members and an outer envelope wall to prevent the arc from taking short-cut paths and thus avoiding one or more of the folded segments of the arc discharge column. Such is not the case in the present invention which avoids these problems but yet which provides a design which is readily manufacturable.